1. Field of the Invention
This invention relates to current transformers, and more particularly to a split core current transformer for use in measuring current flow through current carrying conductors.
2. Description of the Prior Art
In the electrical power industry there is a need to monitor current flow over power conductors for the purpose of load survey and load management, for example. For such purposes, current transformers are used to couple the power conductor to a suitable measuring apparatus, such as a load survey recorder. The installation of a standard instrument transformer usually necessitates interrupting the power circuit and cutting into cabling or busses, requirements which are both undesirable and expensive.
Moreover, in most cases, the measuring apparatus and associated current transformers are installed on a temporary basis while the desired data is recorded and thereafter, the instrumentation is removed. The instrumentation must be re-installed whenever repeat measurements are required.
One known current transformer has been developed which has a split core which permits the transformer to be clamped onto the current carrying conductor to eliminate the undesirable requirements of circuit interruption or cutting into cabling or busses. The transformer has two rectangular core members with a fixed bridge member interconnecting the two core members at first ends and a movable bridge member interconnecting the core members at the other ends, forming a rectangular core structure for the transformer. The movable bridge member is hinged at one end and may be pivoted to open the core structure permitting the transformer to be placed around the conductor.
However, the rectangular core structure of the transformer, which is comprised of two rectangular core members and two bridge members has four separate air gaps in the magnetic path for the transformer. In addition, the core sections are of different configurations, resulting in increased production costs for the transformer. Also, the provision of the hinged bridge member results in a reduced amount of magnetic material in the proximity of the hinge, and as a result adversely influences phase angle accuracy.
Another known split core current transformer employs a pair of generally arcuate core members hinged together at one end with the magnetic path being completed by a butt joint at the other end. While such transformer is of simpler construction than the rectangular split core transformer described above and provides a circular magnetic path which is shorter than that of a rectangular split core transformer of comparable size, the butt joint results in a significant air gap at the junction between core sections such that the transformer is generally unsuitable for applications where repeatability of measurement is required.